Answer: x = (5√2)/2
The last option 
Step-by-step explanation:
The given triangle is a right triangle. Taking angle 45 as the reference angle, 
hypotenuse = 5
opposite side = x
We would find x by applying the sine trigonometric ratio which is expressed as
sin θ = opposite side/hypotenuse
By substituting the given values into the equation, 
sin45 = x/5
Recall, 

Thus, 

x = (5√2)/2
The last option